Re: Pole Pig Simulation

["Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Inductors in the circuit subtract VARS, Capacitors add them.  If they are
all series or parallel, it's fairly easy, but when you have a combination
of both, then, as you've noticed, it gets a tad hairy.

One approach is to convert the series combination of ballast and pig into a
parallel equivalent.  Then, you'll have the PFC C in parallel with the
inductor in parallel with the "resistance" of the pig (actually the TC
load).

The  classic way to do this right is to use complex impedances.  Zl =
Rloss+j*omega*L, Zc =ESRc -j/(omega*C), Xpig = Rpig+jXpig. 

Then, you can use standard series and parallel formulae to figure out the
terminal impedance seen by the power line.

HOWEVER, I suspect that in a TC application, a simple single frequency
impedance calculation won't get a good PF correction.  Why? because the
current is drawn in little bursts when the spark gap fires and the primary
tank charges.  The classic PFC equations all assume sinusoidal voltage and
current.  What you really need to do is calculate V*I at each instant
through the cycle, then average them.  This gives you true power.  Then,
take Vrms*Irms, which gives you apparent power.  The "reactive power" or
"VAR" flow (which doesn't really apply with non-sinusoidal waveforms) is
calculated by

Apparent Power = sqrt(True Power^2 + Reactive Power^2)


The non-sinusoidal nature of the current drawn by a TC is going to be a big
problem with power factor, in much the same way as lightly loaded capacitor
input rectifiers (which only draw power at the peak of the half cycle). PC
switching power supplies caused a lot of problems with this until better
power factors were mandated. The problem was particularly severe in offices
fed by 3 phase Wye, because the neutral currents were quite high (if you
aren't drawing sinusoidal current from the phases, then the neutral
currents don't cancel). This actually resulted in changes to the NEC a few
years back, requiring heavier neutral conductors.

I would venture to say that the PFC might compensate for the ballast, but
isn't going going to compensate for the odd power factor from the sparkgap
and primary tank cap.  For that, you'll need to go to a more sophisticated
circuit.
----------
> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Pole Pig Simulation
> Date: Wednesday, September 06, 2000 6:29 PM
> 
> Original poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net> 
> 
> Hi John C., Terry, 
> 
> I'm having a real difficult time with pole pig simulations for power
> factor. The problem is the ballast. With a pole pig, it will easily draw
> massive amps without any current limiting. I've been reading both your
> responses and continue to integrate these more refined details to the
> similations. 
> 
> With your methods, it necessary to identify the VAR's to calc PF.
However,
> adding either series R, series L, or PFC, the phase angle between line V
> and I change. 
> 
> Is it right to say that the PF could also be calculated this way: 
> 
> (assume 1 cycle here) 
> Identify and the time of zero-crossing of line voltage; 
> Identify the time for zero-crossing of line current; 
> 
> Then,  ARCCOS(Lead time / Lag time) = degree of phase angle? 
> This angle can obvisouly be leading or lagging depending on the circuit. 
> 
> Again, a ballast really makes a mess of this. As L-Ballast is increased,
> the phase angle increases and it also limits current (therefore, any
> current or voltage reading past the ballast cannot be used for
identifying
> a PF based on Volt-Amps or Watts). If the method decribed above will
> perform the same function, then I've got some interesting info about
> ballast PF correction, but if not I could sure use some ideas. 
>   
> 
> HELP!!!!, 
> Bart 
>  
> 
>